The Derlavaian War was fought for six years by the main powers on the continent of Derlavai.
The war began with the death of Alardo, Duke of Bari. With the kingdom without an heir, the kingdom of Algarve moved in to annex it, violating the Treaty of Tortush established at the end of the Six Years' War. The kingdoms of Valmiera, Jelgava, Forthweg, Lagoas, and Sibiu declared war in response to Algarve's actions.
Forthweg drove into northwestern Algarve toward the city of Gozzo, but was quickly driven back by large concentrations of behemoths. Then Unkerlant, seeing an opportunity to regain land it had lost in the previous war, invaded Forthweg from the west. Between the two larger armies, Forthweg fell.
After the defeat of Forthweg a short period of inactivity took place between the warring nations, with Jelgava holding its gains in the Bratanu Mountains in eastern Algarve and Valmiera making only slow advances in the south. Finally Algarve broke the stalemate by driving into northern Valmiera, an area that had been considered too rugged for large operations and therefore weakly defended. Valmiera was conquered in only a month.
Fearing Algarve would pull a similar strategy against them, Jelgavan forces began constructing a series of fortifications along the mountain passes leading into their country. Instead Algarve utilized their air forces by airlifting their troops behind the enemy lines, effectively cutting off the Jelgavan army from its supply lines.
After the defeat of Jelgava, the kingdom of Yanina allied with Algarve, and drove the Lagoans from the Land of the Ice People, while Unkerlant fought a harsh war against Zuwayza in order to regain the lands it lost after the Six Years' War. Algarve did not attempt an invasion of Lagoas, instead invading Unkerlant. The Algarvian-Unkerlanter conflict would witness dramatic Algarvian victories in the first phase that would bring the Algarvians to the gates of the Unkerlanter capital, Cottbus, but winter and logistics would lead to the thwarting of the Algarvian victory, followed by major Unkerlanter drives. It was during this phase that the Algarvians first began to turn to the use of "Special Magecraft": mass slaughter of Kaunians to secure a desperate weapon of "mass destruction to boost their own power.
In the wake of this, the Algarvians were to initiate a second campaign to destroy Unkerlant, this one meeting a harsh fate in the gruesome battle for the city of Sulingen on the Wolter, beginning with a dramatic Algarvian victory, and ending with the complete destruction of an army marooned in a bloody battle in the city and some of the most costly and savage battles within the overall war. This campaign wrecked the best portions of Algarve's remaining army, and was subsequent with the destruction of the army in the Land of the Ice People following an attempt to export the massacres of Kaunians done against the will of the locals and the Gods these locals served.
The next year, Algarve tried once more to destroy Unkerlant, only to be caught up in the colossal Battle of the Durrwangen Bulge, which destroyed Algarve's ability to use behemoths to the same degree as Unkerlant and was one of the largest and the most destructive conflicts of the entire Western Front. Durrwangen was not a triumph of skill but instead a brutal slamming match between two giants where one giant broke but the other kept on striking. After the war in the Land of the Ice People, the Eastern Front settled for a time into a pattern of ever larger raids of dragons on Derlavai's East, and on the frantic work done by the Nantaali Project. Also in the West, Kuusamo and Gyongyos fought bitter battles over islands that were marked by costly offensives over limited territory.
The next year, the Unkerlanters would begin a set of colossal offensives that took the Algarvians ever further down the abyss, and took the Unkerlanters themselves into Algarve, with Gyongyos beginning to use the bloody magic pioneered by Algarve, the controversial Eoforwic Uprising, and the Unkerlanters securing the switches of Zuwayza and Yanina to their side in the titanic Western Front. As Algarve's situation declined, the Unkerlanter Army was soon to amass an advantage so powerful that even the death of skillful Behemoth riders like General Vatran could not redress the losses these armies suffered. Soon, too, the Eastern Front heated up with the invasion of Jelgava, and with this the slow unraveling of Algarve's control of Valmiera.
In the last year of the war, the bloody Battle of Trapani ended with the suicide of Algarve's King Mezentio and the unleashing of the demonic Powers Below in last-ditch and ultimately failed gambits to postpone Algarve's defeat, in the meeting of the Unkerlanters and the Kuusamans and Lagoans in the eastern portion of Algarve, the division of the continent, and the use of the new and deadly magic developed by the Nantaali Project that annihilated Gyongyos. With the annihilation from the skies of Gyorvar, Gyongyos's capital, the Derlavaian War came to an end and a continent was suspended between the Empires of Kuusamo in the East and Unkerlant in the West.
- World War II, on which the Derlavaian War appears to be based.